Influence of pulmonary endothelial cells on fetal lung development.

Culture medium conditioned by pulmonary endothelial cells stimulated proliferation of cultured fetal lung cells, as measured by increases in cell numbers, incorporation of tritiated thymidine into DNA, and incorporation of labeled choline into membrane phospholipids. Medium conditioned by several other cell culture preparations of fetal lung did not elicit these effects. The growth-promoting activity was found to be concentrated in fractions of 42,000 and 89,000 molecular weight (mol wt). In addition to promoting cell growth, medium conditioned by pulmonary endothelial cells also appeared to stimulate the incorporation of labeled choline into surfactant-associated phosphatidylcholine. These results suggest that pulmonary endothelial cells may produce factors that stimulate the growth and perhaps also the differentiation of fetal lung cells in culture.